The microelectronic industry is continually striving to produce ever faster and smaller microelectronic devices for use in various electronic products, including, but not limited to portable products, such as portable computers, digital cameras, electronic tablets, cellular phones, wearable electronics, applications for the Internet of Things, and the like. As the size of the microelectronic devices is reduced, it becomes more difficult to attach these microelectronic devices to microelectronic substrates in order to form electrical interconnections between various components.
One solution for the attachment issue would be to fabricate the microelectronic substrate entirely with high density electrical routing, as will be understood to those skilled in the art. However, such high density electrical routing requires expensive lithography processes, which can cost between 10 times to 50 times more than standard lithography processes used for fabricating lower density substrates, such as printed circuit boards. Another solution would be to fabricate an interposer, such as a silicon interposer, to position between the microelectronic device and the microelectronic substrate. Such interposers can be used to connect the microelectronic device to the microelectronic substrate by providing electrical routes that are high density in the area of the microelectronic device and which spread or fan out through the interposer to a lower density at the microelectronic substrate. However, such interposers can reduce electrical performance and may increase the height or thickness of the resulting microelectronic structure. Therefore, there in a need to develop microelectronic substrates which can economically provide both high density and low density interconnections.